stupid yoke insall question

When I installed the yokes on my 205 used the nuts supplied by ORD but also a large washer. Is there supposed to be any washer used or just the nut to hold the yoke down? And if it is just the nut, I'm assuming the flat side goes against the yoke right?

Reason for asking is I now have a speed dependent vibration with the new t-case and brand new shafts when I never used to have any vibes at all, and was thinking maybe the yokes were installed improperly.

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